1. Field of the Invention
The present invention relates to a liquid crystal display device used as a display device for computers, audiovisual equipment and the like.
2. Description of the Related Art
Japanese Laid-Open Publication No. 10-186330 discloses a liquid crystal display device in which liquid crystal molecules are axially symmetrically aligned in each of pixel regions in the presence of applied voltage. Such a liquid crystal display device can provide a display with wide viewing angle characteristics and satisfactory contrast.
FIG. 6B is a top plan view of a liquid crystal display device 100 having the above-described structure. FIG. 6A is a partial cross-sectional view of the liquid crystal display device 100 taken along a line Y-Yxe2x80x2 of FIG. 6B. In the liquid crystal display device 100, a transparent electrode 63 is formed on a substrate 62. A protrusion 66 approximately 3 xcexcm high (liquid crystal molecule alignment limiting arrangement) is formed outside a plurality of pixel regions 69. Spacers 65 approximately 5 xcexcm high are formed of photosensitive polyimide on the protrusion 66. A vertical alignment layer 68 is formed on the transparent electrode 63 so as to cover the protrusion 66 and the spacer 65 by spin-coating. The vertical alignment layer 68 is formed of JALS-204 (Japan Synthetic Rubber Co., Ltd.). Another vertical alignment layer 68 is formed of the same material on the other substrate (not shown).
The pixel regions 69 surrounded by the protrusion 66 each have a size of approximately 100 xcexcmxc3x97100 xcexcm. The liquid crystal molecules in a liquid crystal layer (not shown) are axially symmetrically aligned in each of the pixel regions 69 in the presence of applied voltage.
In the liquid crystal display device 100, an alignment fixing layer is provided by curing a photocurable resin, which has been previously mixed with a liquid crystal material, while applying a voltage in order to stabilize the axially symmetric alignment of the liquid crystal molecules. Acrylate resins, methacrylate resins, styrene resins, and derivatives thereof can be used as the photocurable resin.
However, the arrangement of the liquid crystal display device disclosed by Japanese Laid-Open Publication No. 10-186330 described above has, for example, the following disadvantages: 1) the use of the photocurable resin increases cost; 2) the number of steps of fabricating the liquid crystal display device is increased since the alignment fixing layer is provided by curing the photocurable resin by illuminating with ultraviolet light while the liquid crystal molecules are kept axially symmetrically aligned in the presence of applied voltage across the liquid crystal layer; and 3) the ultraviolet light used for fixing the alignment of the liquid crystal molecules partially decomposes the liquid crystal material, causing reduction in a voltage retaining ratio, thereby resulting in deterioration of image display reliability (e.g. image sticking).
On the other hand, unless the alignment fixing layer is provided, there occurs a problem that a response time is slow.
A liquid crystal display device according to the present invention includes a first substrate, a second substrate, and a liquid crystal layer interposed between the first and second substrates. The first substrate includes a protrusion structure and a vertical alignment layer each facing the liquid crystal layer. The liquid crystal layer includes a plurality of liquid crystal regions separated from each other by the protrusion structure. Liquid crystal molecules in the plurality of liquid crystal regions are aligned axially symmetrically around an axis perpendicular to a surface of the second substrate at least in the presence of applied voltage. Each of the plurality of liquid crystal regions has a size such that each of the plurality of liquid crystal regions is included within a circular area circumscribing a square of approximately 70 xcexcm or less.
In one embodiment of the invention, the plurality of liquid crystal regions are contained in a single pixel region.
In one embodiment of the invention, the protrusion structure is arranged in a grid pattern.
In one embodiment of the invention, the protrusion structure is arranged in a checkered pattern.
In one embodiment of the invention, the liquid crystal regions surrounded by the protrusion structure are polygons.
In one embodiment of the invention, the liquid crystal regions surrounded by the protrusion structure are polygons of different sizes, and are regularly arranged.
In one embodiment of the invention, the protrusion structure is made of a transparent material.
In one embodiment of the invention, a height of the protrusion structure is approximately 2 xcexcm or less.
In one embodiment of the invention, a response time is approximately 60 ms or less.
In one embodiment of the invention, the liquid crystal regions surrounded by the protrusion structure are squares.
In one embodiment of the invention, the second substrate is a plasma cell. The second substrate includes a plate, a dielectric sheet, ribs and discharge channels. The discharge channels are arranged in rows and each discharge channel is surrounded by the ribs interposed between the plate and the dielectric sheet. The protrusion structure is provided between the first substrate and the dielectric sheet.
Hereinafter, functions of the present invention will be described.
In the liquid crystal display device of the present invention, the size of each liquid crystal region separated by the protrusion structure provided in the substrate is a size such that each liquid crystal region is included within a circular area circumscribing a square of approximately 70 xcexcm or less. Therefore, stable axially symmetric alignment can be established in each liquid crystal region, and a sufficiently high response speed (sufficiently short response time), e.g., approximately 60 ms or less, is obtained. Furthermore, in the case where the above size is a size such that each liquid crystal region is included within a circular area circumscribing a square of approximately 50 xcexcm or less, a higher response speed, e.g., approximately 55 ms or less, is obtained.
A pixel region may contain a plurality of liquid crystal regions separated from each other by the protrusion structure, whereby the liquid crystal display device of the present invention can have large pixel regions. Furthermore, the modification of the shape and size of the protrusion structure can lead to change in the size of the liquid crystal region.
The protrusion structure may be arranged in a grid pattern or in a checkered pattern, whereby a high aperture ratio can be obtained.
The regions surrounded by the protrusion structure may be polygons having different sizes and the polygons are regularly arranged, whereby the aperture ratio can be greater than that of a grid or checkered pattern.
The protrusion structure may be made of a transparent material, whereby light passes through the protrusion structure to the liquid crystal layer, contributing to an increase in the transmittance of the whole liquid crystal layer.
The height of the protrusion structure may be approximately 2 xcexcm or less, more preferably about 1 xcexcm or less, whereby the liquid crystal layer in a region interposed between the protrusion structure and the counter substrate (not the liquid crystal region) has nearly the same thickness as that of the region surrounded by the protrusion structure. Therefore, the display characteristics of both regions are close to each other.
It is not necessary to restrict the type of a drive element in the liquid crystal display device of the present invention. In the case where a plasma generating substrate is adopted, however, significant effects can be realized in a large liquid crystal display device.
Thus, the invention disclosed herein makes possible the advantage of providing a liquid crystal display device in which liquid crystal molecules are stabilized without any alignment fixing layer, and a sufficient response speed is obtained.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.